1. Field of the Invention
The present invention relates to an energy conservation and refrigeration control system for chilled-product vending machines. More specifically, the present invention relates to a control circuit for a forced air type refrigeration system for a vending machine which dispenses chilled products such as beverage cans or bottles.
2. Description of the Prior Art
Heretofore, in refrigeration systems of vending machines including a compressor, a condensor, condensor coil, condensor fan motor, evaporator coil and an evaporator fan, the compressor has been cycled ON and OFF under the control of a thermostat, and the evaporator fan, which blows air over the evaporator coil to circulate chilled air throughout the vending machine, has been run continuously even during the periods when the compressor was OFF. The unnecessary high energy useage and waste caused by the continuous running of the evaporator fan or fans, has become a problem with the current high cost of energy. One logical solution to reducing the consumption of energy is to cycle the evaporator fan motor ON and OFF with the compressor thus decreasing the running time of the evaporator fan. However, this approach causes several problems, which have been discussed in co-pending U.S. application Ser. No. 198,172 filed Oct. 17, 1980 by Morgan and King and assigned to the same assignee as the present invention. Application Ser. No. 198,172 stands abandoned in favor of Continuation Application Ser. No. 466,959, filed Feb. 16, 1983 which is now U.S. Pat. No. 4,467,617.
Firstly, if the evaporator fan is cycled off in synchronism with the turning OFF of the compressor, freeze-up of the evaporator coil can occur in humid, high temperature conditions. Secondly, by keeping the evaporator fan shut off during the compressor off cycles, large variations in temperature in the vending machine occur, creating large variations in temperature of the next to be vended products. Also, during this off period of the evaporator fan, large variations of temperature occur throughout the vending machine due to lack of air flow, and temperatures sensed by the thermostat which controls the compressor cycling are less accurate than desirable. Thirdly, when vending machines are located in below freezing environments (32.degree. F.), an idle condition of the evaporator fan may permit the chilled products to freeze. That is, when the evaporator fan is running and blowing air over the evaporator coil and throughout the vending machine, this flow of air dissipates heat generated by the evaporator fan motors thus acting as a heater to prevent the stored products from freezing. Thus, the aforementioned problems exist when the evaporator fan is permitted to cycle on and off with the compressor, even though a substantial reduction in energy consumption results.
Accordingly, prior to the invention described in the aforementioned co-pending application of Morgan, et al., a need in the art existed for a system which would reduce the consumption of energy in the refrigeration system of a vending machine, but at the same time solve the aforementioned problems of evaporator coil freeze-up in high, humid temperature conditions; product freeze-up in below freezing environmental conditions; and large variations in next to be vended products and temperature distribution throughout the vending machine. In the system invented by Morgan, et al. these functions are controlled by electromechanical timers which vary the operating cycle of the evaporator fan to effect a solution to the aforementioned problems.
A modification of the Morgan, et al. system for effecting the same and additional controls for refrigeration systems of chilled-product vending machines was implemented by use of a microprocessor. These modifications are described in co-pending U.S. application Ser. No. 363,961 filed Mar. 31, 1982 by Morgan and King assigned to the same assignee of the present invention, which is now U.S. Pat. No. 4,417,450.
The disclosures of the aforementioned U.S. applications Ser. Nos. 198,172 and 363,961 to Morgan, et al. are incorporated herein by reference.